Centrifugal spray coating methods and apparatus



July l5, 1969 J. Klwlr-:T 3,455,728

CENTRIFUGAL SPRAY COATING METHODS AND APPARATUS 5 Sheets-Sheet 2 A'rrYs.

July 15, 1969 J. KlwlET CENTRIFUGAL SPRAY COATING METHODS AND APPARATUS Filed Oct. 4. 1965 J. KIWiET July 15, 1969 CENTRIFUGAL SPRAY COATING METHODS AND APPARATUS Filed Oct. 4, 1965 5 Sheets-Sheet 3 FLUID, SOURCE INVENTOR JoHANNES KlwlET AT1-Ys.

United States Patent O 3,455,728 CENTRIFUGAL SPRAY COATING METHODS AND APPARATUS Johannes Kiwiet, Riverside, Ill., assignor to Inland Steel Company, Chicago, Ill., a corporation of Delaware Filed Oct. 4, 1965, Ser. No. 492,682 Int. Cl. Bc 7/02; B44d 1/08 U.S. Cl. 117-96 5 Claims ABSTRACT OF THE DISCLOSURE The present invention relates generally to spray coating methods and apparatus and, more particularly, to an improved centrifugal spray coating system of the type commonly employed in coating the internal surface of a hollow workpiece such, merely by way of example, as a cylindrical shell which may ultimately comprise the sidewall of a container or the like. In its principal aspects, the invention is concerned with improved centrifugal spray coating methods and apparatus characterized by their ability to rapidly coat a workpiece surface with a material such as paint, lacquer, rust inhibitor, or other material in a liquid or semiliquid state, yet wherein the coating applied to such surface is characterized by its uniformity and freedom from gaps or voids in the region of surface irregularities, contours, openings and the like.

In the field of centrifugal spray coating equipment, it has long been recognized that if a liquid or semiliquid spray material, for example, paint of the like, is applied to a rotating disc at or near the center thereof, such material will flow radially toward the outer periphery of the disc because of the effect of centrifugal force and, assuming that the centrifugal force is suiciently great, the particles of spray material will be projected from the periphery of the disc at a definite velocity. It has further been recognized that a practical spray system requires that the size of the centrifugally projected particles not exceed a known level. At the same time, however, such a system must be capable of discharging, within an allotted period of time, a quantity of material sufficient to coat the entire surface of the workpiece to be coated and, of course, such coating should be of uniform thickness throughout.

Experiments have demonstrated that the size of centrifugally projected particles is a function of numerous conditions, including, but not limited to (l) the viscosity a and adhesive properties T of the material being sprayed, (2) the tangential velocity at the outer periphery of the spray disc, (3) the thickness of the layer of spray material at the outer periphery of the spray disc, and (4) the shape of the outer periphery of the disc. Obviously, however, once a particular spray material has been selected, the viscosity n and adhesive properties T of that material are fixed and will not vary. Similarly, for a given spray head, the tangential velocity at the outer periphery of the disc will depend upon the diameter of the disc and the rotational speed w thereof. Again, once the disc has been selected and the maximum operating speed determined, the factor of tangential velocity will not vary, assuming, of course, that the spray head is being operated at its op- "ice tirnum operational speed. As to the thickness of the layer of spray material at the periphery of the disc, it has been found that this is a function of the amount of material fed to the disc. Since it is essential that the maximum particle size be controlled, it then becomes apparent that the maximum thickness of the spray material at all points about the periphery of the disc must be controlled. Preferably, such thickness should be uniform or substantially uniform about the peripheral edge of the disc in order to permit maximum application of the spray material to the workpiece without exceeding the maximum layer thickness at any point. Finally, it has been found that particle size can be controlled by forming the disc with a relatively sharp outer peripheral edge, thereby minimizing the tendency of particles to adhere to the disc.

Because of the foreging limitations, imposed by virtue of the requirement that particle size of the spray material not exceed a maximum value, a spray device employing only a single spray disc has a limited capacity in terms of volume of material sprayed per unit of time and, consequently, in terms of area of coverage. It has, however, heretofore been proposed that the capacity of a disc-type centrifugal spray head can be increased by the simple expedient of providing a plurality of axially spaced, coaxial, parallel discs and simultaneously applying the spray material to each of such discs at or adjacent the central portions thereof. Consequently, as the discs are rotated, the spray material ows radially outward on each disc and is projected therefrom by the centrifugal forces developed. A typical example of such a conventional prior art construction is that shown in U.S. Patent No. 2,545,488 to E. O. Norris. Unfortunately, however, conventional centrifugal spray devices of the multidisc type have not provided a completely satisfactory solution to the problem of rapidly applying a uniform coating to a workpiece. One principal reason for this has involved the diiculty and, indeed, inability to apply equal quantities of the spray material uniformly to each of the discs. Even in those iustances where equal quantities of material have been fed to each disc, it has been found that the material is not uniformly applied to one or more of the discs and, consequently, the centrifugally projected particles of spray material emanating from the discs are not uniform in size. As a result, the coating applied to the workpiece is not uniform and often assumes a speckled or dimpled appearance similar, for example, to that found on an orange skin.

There is disclosed and claimed in copending application Ser. No. 460,798, iiled June 2, 1965, assigned to the assignee of the present invention, centrifugal spray coating methods and apparatus for uniformly coating the internal surface of a cylindrical shell which may be advantageously utilized with the present invention. Such application further discloses and claims an improved centrifugal spray device of the multidisc type wherein each spray disc irrespective of the number of discs employed, has applied thereto a circumferentially continuous substantially uniform coating of spray material for centrifugal projection of a peripherally uniform band or annulus of spray material. The arrangement is such that the spray material is applied continuously and uniformly to the rotating discs whereby it ows outwardly along substantially radial lines under the influence of centrifugal force. Consequently, particles of spray material are centrifugally projected from the outer peripheral edge of each spray disc with the coating applied to the work surface being uniform and smooth throughout its entire area.

`Consistent with the problem heretofore experienced regarding lack of uniformity of coating application, it has also been recognized that particles of spray material are centrifugally projected from the spray discs along lines generally tangent to the outer peripheral edge of the discs and in a direction opposite to the direction of rotation of the discs. As a consequence, surface irregularities, contours, openings or the like present obstructions in the tlow paths of spray particles which create gaps or voids in the coating being applied. Moreover, ghosting or thinned areas of spray material can occur on eclipsed areas about surface irregularities or contoured portions of the work surface.

It is a general aim of the present invention to provide an improved centrifugal spray coating system which overcomes the foregoing disadvantages and which is characterized by its ability to rapidly vapply a uniform coating of spray material while avoiding gaps, voids, or ghosting on the surface of the workpiece to be coated. While not so limited in its application, the invention will nd especially advantageous use in applying a uniform coating to the internal surface of cylindrical shells such, merely by way of example, as the cylindrical sidewall of a SS-gallon shipping drum of the type commonly made from sheet steel or other suitable material.

In accordance with another of the important aspects of the present invention, it is an object to provide improved methods and apparatus for spray coating a work surface characterized by their versatility and which readily permit effective use thereof in internally coating cylindrical workpieces which may vary widely in diameter from workpiece to workpiece. In this connection, it is an object to provide a simple, reliable centrifugal spray coating system particularly suitable for use in mass production operations.

Yet another important aspect of the present invention is to provide an improved multidisc type centrifugal spray device for internally coating cylindrical workpieces wherein the spray material is uniformly distributed to all of the discs by a distributor yet wherein only the rotating distributor need be varied slightly for providing uniformly distributed material to discs of an oppositely rotating spray device. As Ia consequence of obtaining this objective, centrifugal spray devices embodying the features of the invention are characterized by their ease of manufacture, reliability in operation, and by the fact that only minimum maintenance is required.

Other objects and advantages of the invention will become apparent as the following description proceeds, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a fragmentary, and partially diagrammatic, elevational view of an exemplary centrifugal spray system for applying internal coatings to a cylindrical shell embodying the features of the present invention;

FIG. 2 is a fragmentary plan View, here depicted an exemplary cylindrical shell in phantom, together with a portion of the apparatus shown in FIG. 1 for moving the shell relative to a spray head embodying the features of the present invention so as to cause the latter to relatively traverse the inner shell surface during a spray coating cycle;

FIG. 3 is a fragmentary side elevation, in vertical half section, of an exemplary centrifugal spray coating device used in conjunction with the spray system of the present invention;

FIG. 4 is an end View of an exemplary material distributor used in conjunction with the spray coating devices shown in FIG. 1 here illustrating the distributor intended for counter clockwise rotation;

FIG. 5 is a side elevation of the material distributor shown in FIG. 4;

FIG. 6 is an end view of an exemplary material distributor similar to FIG. 4, but here illustrating the distributor intended for clockwise rotation;

FIG. 7 is a side elevation of the material distributor shown in FIG. 6;

FIG. 8 is a fragmentary end view of a portion of the material distributor and one of the annular spray discs,

4 here diagrammatically illustrating the distributional pattern of spray material as the latter is distributed to the spray disc and to the workpiece; and,

FIG. 9 is a fragmentary, and partially diagrammatic View, similar to FIG. l, but here depicting a slightly modified centrifugal spray system also embodying the features of the present invention.

While the invention is susceptible of various modifications and yalternative forms, specific embodiments thereof have been shown by Way of example in the drawings and will herein be described in detail. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but, on the contrary, the intention lis to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as expressed in the appended claims.

Referring now to the drawings, there is diagrammatically illustrated in FIG. l an exemplary centrifugal spray coating system generally indicated at 10, which is particularly suitable for coating the internal surface of cylindrical shells 11, 12 on a mass production basis and in accordance with the present invention. While the particular type or workpiece to be coated is not critical to the present invention, it will be appreciated as the ensuing description proceeds, that the exemplary spray coating system 10 shown in FIG. l will find particularly advantageous, but by no means exclusive, use in coating the internal surface of a cylindrical shell such as the sidewalls of conventional SS-gallon shipping containers which can be made of sheet metal or any other suitable natural or synthetic sheet material.

As here illustrated cylindrical shells 11, 12 are fed to spray coating stations, generally indicated at 14, 15 in seriatim order, by means of a conveyor belt 16 or the like. The particular means for driving the conveyor belt are not critical to the present invention, and may take any of a wide variety of conventional forms well known to those skilled in the art. It should sullice to say that the drive system for the conveyor belt is such that control means are provided for automatically moving the belt to transfer shells from work station to work station, and for intermittently stopping the belt as successive shells reach each work station so as to permit performance of an operational cycle. In the present instance, in order to insure that the shells 11, 12 are properly alined with each different work station, for example, the spray coating station 14, the belt is provided with a plurality of positioning lugs 18 which serve to accurately position the shells at predetermined points on the conveyor belt 16.

For the purpose of applying a uniform coating to the work surface, and as =best shown in FIG. 3, the exemplary centrifugal spray device 2i) includes a rotable spray head, generally indicated at 22, which is rigidly secured to one end of a drive shaft 24 by any suitable means such, for example, as a threaded connection 25. In the illustrative construction, the drive shaft 24, which is coupled to any suitable power source (not shown) for elfecting rotation thereof, is rotatably supported coaxially within a cylindrical sleeve 26 by means of spaced bearings, there being one such bearing 28 shown in FIG. 3. As the ensuing description proceeds, it will become apparent to those skilled in the art that during a spray coating operation the spray device 20 can be either held stationary in an axially fixed position while the workpiece is translated in an axial direction relative to the spray head 22., or, alternatively, the workpiece can be held stationary while the spray head is translated in an axial direction. In the iirst instance, the support sleeve 26 is preferably rigidly secured to a fixed structural member (not shown) while, in the second instance, suitable power means (not shown) must be provided for effecting controlled axial movement of the sleeve 26 and, consequently, of the rotating spray head 22 during a spray coating operation.

In order to permit distribution of the liquid or semiliquid spray material on the surface of the workpiece to be coated, the exemplary spray head 22 includes an assembly of identical axially spaced, annular spray discs D1-D8, which are rigidly clamped between a pair of disc-like plates 29, '30, having an external diameter equal to the diameter of the discs D1-D8. In the illustrative form of the invention, the plate 29 includes a hub portion 31 which is rigidly mounted on the driveshaft 24 for rotation therewith. A pair of axially directed tubular sleeves (there being one such sleeve 32 visible in FIG. 3) are positioned within counterboxes 34 formed at diametrically opposed points in the plate 2'9 adjacent the outer peripheral edge thereof, the sleeves 32 here passing through apertures formed in the discs D1-D8 and thus serving to support the latter in parallel relation to one another and concentrically about the shaft 24. The arrangement is such that washer-like spacers 35 positioned on the sleeves 32 between the adjacent discs serve to axially space the latter from one another and from the plates 29, 30. In the exemplary construction, the plates and discs are rigidly held together as a unitary assembly by means of threaded fasteners 36 which are here threadingly coupled to opposite ends of the tubular sleeves 32. Thus, when the fasteners 36 are tightened, the plates 29, 30 and discs Dl-DS are drawn axially towards one another to form a rigid assembly of axially spaced spray discs which are rotatably driven by the shaft 24.

For the purpose of supplying liquid or semiliquid spray material to the discs, the exemplary spray head 22 includes a centrally disposed distributor 38 which is concentrically supported within the annular spray discs Dlt-D8 and rigidly mounted on the shaft 24 for simultaneous rotation with the shaft and discs. As best shown by reference to FIGS. 3, 4 and 5 conjointly, the distributor 3S includes a hub portion 39 having an annular charge cavity 40 formed therein, and a plurality of generally axially extending, outwardly iiared, `distributor teeth 41 disposed outwardly of the cavity 40 but within the confines of the annular spray discs D1D8. The arrangement is such that the spray material, which is normally maintained in a supply reservoir 42 (FIG. 1), is delivered under pressure by means of one or more pumps 44 (FIG. 1), through one or more injection nozzles 45, the latter here being supported on a collar 46 mounted on the support sleeve 26, directly into the charge cavity 40 in the distributor 38.

As a consequence of the foregoing construction, during a spray coating operation particles of the spray material delivered to the cavity 40 are moved outwardly (i.e., upwardly as viewed in FIG. 3) along the teeth 41 due to the effect of centrifugal force, with the particles of material being centrifugally projected outwardly from the teeth in substantially radial planes towards the inner peripheral edges of the discs D1-DS. It has been found that once particles of spray material are applied to the inner peripheral edges of the discs Dl-DS, such particles proceed or flow outwardly towards the outer peripheral edges of the discs along substantially radial lines under the influence of centrifugal force. As a consequence, in those instances where the particles are applied to peripherally spaced localized points on the inner peripheral edges of the discs, the particles will not be uniformly distributed about the discs, but rather will be concentrated in localized areas which are radially related to the points on the inner peripheral edges of the discs where the material is applied. Consequently, gaps are present on the discs between such points where little, if any, spray material is present. Therefore, those portions of the discs which do not receive particles of spray material do not contribute in any signicant way, if at all, to the capacity of the spray device 20. Stated another way, and keeping in mind that the thickness of the layer of spray material on any given disc must be controlled so as not to exceed a maximum thickness, thereby preventing projection of excessively large droplets of material which would tend to speckle the surface of the workpiece, it will be appreciated that rwhere the entire surface of a given disc is uniformly and continuously coated with the spray material such a disc is capable of projecting a maximum quantity of spray material in a given period of time. However, when only circurnferentially spaced areas of the disc are coated, the quantity of spray material delivered to such disc must be less or else the thickness of the coated areas will exceed the maximum thickness permissible, thereby leading to speckling of the coated workpiece.

Provision is made for insuring that substantially equal quantities of spray material are delivered to each of the spray discs D1-D8 while at the same time the spray material delivered to each disc is applied substantially continuously and uniformly about the inner peripheral edge of that disc, thereby precluding the presence of voids or gaps in the particles of spray material applied to each disc. In order to accomplish this, and as best illustrated by reference to FIG. 8, advantage is taken of the fact that as particles of spray material leave a given point P on each tooth, such particles form bands of spray material which move substantially radially, outward through the gap between the teeth 41 and the inner peripheral edges of the discs, such bands being represented in FIG. 8 by the reference numeral 48. It has further been found that the bands 48 of spray material, which bands lie in planes parallel to the planes of the discs, tend to increase in width as they get further from the point P of discharge from the teeth and closer to the inner peripheral edge of the adjacent disc. Keeping the foregoing in mind, it will be observed upon inspection of FIG. 8 that as particles of spray material leave points P on all of the teeth 41, which points are radially inward of a given `disc D, such particles form a plurality of bands 48 which gradually increase in width and merge or blend into one another as the particles reach the inner peripheral edge of the disc D. Thereafter, the particles proceed outwardly on the disc along substantially radial lines under the effect of centrifugal force, with the particles ultimately being projected outwardly from the outer peripheral edge of the disc D into engagement with the adjacent surface of the workpiece to be coated (not shown). In this instance, however, since the inner peripheral edge of the disc D is spaced from the points P by a radial distance sufficient to permit merging or blending of the bands 48, the entire surface of the disc D is coated with spray particles--that is, the spray material is continuously and substantially uniformly applied to the inner peripheral edge of th disc.

The centrifugal spray heads are arranged so that the radial gap between the distributor teeth 41 and all of the discs Dl-DS is sufficiently great to insure that the spray material is applied continuously about the inner peripheral edges of all of the discs, thereby preventing the presence of localized areas yon any given spray disc which are not coated with the spray material. It will, of course, be appreciated by those skilled in the art that the actual radial dimensions of the gaps between distributor teeth 41 and spray discs Dl-DS may vary widely dependent upon various factors such as the dimensions of the spray discsv and the distributor head, the rotational speed w of the spray head, and the viscosity n and adhesive properties T of the particular spray material. However, it has been found that in the typicalV spray head described and intended for use in coating the interior surface of a conventional 55-gallon shipping container with a viscous material such as paint or the like, and where the spray head is operating at a speed of approximately 7,000 r.p.m., the minimum radial gap between the distributor teeth 41 and any given disc (e.g., disc D8 in FIG. 3) should be on the order of approximately one inch. Similarly, it has been found that under the foregoing conditions, the maximum radial gap between the distributor teeth 41 and any given disc (for example, the disc D1 in FIG. 3) should be on the order of one and one-half inches. Thus, under these conditions, it has been found that the particles of spray material are applied continuously about all of the discs, since the radial gap provided is sufficient to permit merging or blending of the bands of spray material emanating from adjacent teeth at or just prior to the time the bands reach the inner peripheral edge of the discs. That is to say, under these conditions, FIG. 8 is representative of the pattern of spray material applied to the disc D8. As for the remaining discs D1-D7 (which discs are all spaced radially further from the teeth 41 than is disc D8), the adjacent bands 48 of spray material will tend to overlap slightly on the spray discs. However, it has been found that such overlap does not appreciably affect the uniformity of the coating applied to the workpiece, whereas gaps present on one or more of the discs do tend to aifect the uniformity of the coating applied to the workpiece.

For a further understanding of the details of the radial gaps, reference is made to the aforesaid copending application Ser. No. 460,798, filed June 2, 1965. It can, thus, be seen that spray heads constructed so that the radial gap between the distributor teeth and all discs is sufliciently great to permit merging or blending of the bands of spray material emanating from those points on the distributor teeth lying in a common radial plane at or before the time that such bands are applied to the adjacent spray disc-will permit the application of spray material substantially uniformly and continuously to all discs, thereby insuring that substantially the entire surface area of each disc is coated with spray material. Under such conditions, it is possible to inject spray material into the spray head at the full rated capacity of the spray head 22 while still insuring that the size of the particles of spray material projected from the discs are substantially uniform from disc to disc and do not exceed a predetermined level. Consequently, the coating applied to the workpiece is characterized by its uniformity and smoothness throughout its entire surface area. Because of the foregoing, it is also possible to coat a given surface area to a prescribed thickness in considerably less time than has been previously possible.

It will, of cou-rse, be understood from the foregoing that a critical feature of the spray head resides in the proper selection of radial gaps between the distributor teeth 41 and the spray discs D1-D8, which gaps may vary dependent upon the nature of the material being applied and the size and operating speed of the spray head. Such gaps must be sufficiently great to insure that the spray material is applied continuously about the inner peripheral edge of that disc which is closest to the distributor 38. The maximum permissible radial gap is considerably less critical, it being understood that such gap must be sufficiently small to permit manufacture of a spray head which will fit within the workpiece to be coated. Moreover, it is desirable that the radial gap be kept as small as practical in order to insure that the particles of spray material do not slow down to a point where they lose proper directivity and are not uniformly distributed on the disc.

In order to apply a uniform annular band of spray material to the interior surfaces of cylindrical shells which may have any one of a wide range of different diameters, yet wherein this can be accomplished with the same basic spray head and associated equipment it ,has been found that where a centrifugal spray head is used to apply a uniform annular band of spray material to the interior surface of a shell (e.g., the shell 11 depicted in FIG. l), it is essential that the particles of spray material be projected from the outer periphery of the spray discs D1-D8 with` a motion in the plane of the discs, Such particles must then flow toward the shell 11 without deviating significantly from such plane. Consequently, it is necessary to dimension the spray discs so that the outer peripheral edges of the latter are in close spaced proximity to the surface being coated. Absence of such close dimensional proximity between the outer peripheral edges of the spray discs and the surface being coated results in air turbulence in the vicinity of the spray head 22, and such turbulence tends to urge the particles of spray material out of their intended planes of motion, with consequent nonuniform coating of the product. For this reason, it has been found necessary to utilize a different sized spray head with each significantly different sized shell diameter.

Accordingly, provision is made for shielding the spray head 22 from the effect of air turbulence, thereby permitting use of a single spray head with a wide range of different diameter shells even though there may be a significant radial gap between the outer peripheral edge of the spray discs Dl-DS and the interior surface being coated. To accomplish this, and as best illustrated by reference to FIG. 3, the exemplary spray head 22 is provided with a pair of removable annular skirts 51, 52 which are respectively secured to the outer surfaces of the plates 29, 30 by means of the threaded fasteners 36. As here shown, the skirts 51, 52 are considerably greater in diameter than are the plates 29, 30 and the discs D1-D8. As a consequence of this construction, it is merely necessary to employ relatively inexpensive skirts which are slightly smaller in diameter than is the internal diameter of the surface being coated, and such skirts will effectively eliminate the tendency for air turbulence to aect the path of movement of particles of spray material flowing from the spary head toward the surface being coated. Therefore, when the spray device 20 is being utilized to coat the inner surface of a shell having either a smaller or a larger diameter than that of the skirts 51, 52 it is merely necessary to remove the skirts 51, 52 and replace such skirts with either smaller or larger skirts respectively, thereby permitting effective use of a single spray head with different sized shells and further enhancing the uniformity of the coating applied thereto.

In carrying out the present invention, provision is made for insuring that a uniform coating of spray material is applied to the interior surfaces of cylindrical shells while at the same time precluding the presence of voids, gaps or thinned areas particularly regions about surface irregularities, contours or openings in the work surface. In order to accomplish this, advantage is taken of the fact that particles of spray material are projected outwardly from the outer peripheral edge of the spray head discs D 'along lines generally tangent to the discs and in a direction opposite to the rotational direction of the discs. As best shown in FIG. 8, it will be observed that particles of spray material centrifugally projected outwardly from points S along the outer peripheral edge of the disc D (rotating in the direction shown) will ilow toward the interior surface of shell 11 along lines 53 angular to the surface to which the particles are applied. In a container sidewall, for example, with a bung hole 54 formed therein the spray would not be applied at surface 5S. As a consequence, in those instances where surface irregularities or the like are present little, if any, spray material will be applied in some regions of the irregularity. Keeping the foregoing in mind, a centrifugal spray system in accordance with the present invention, is arranged so that the spray material is applied continuously about the internal surface of the shell with spray particles applied at a rst direction and subsequently applying spray particles from a direction opposite to the rst direction, thereby preventing the presence of regions which are not coated with the spray material.

In carrying out this form of the invention, referring to FIG. l, a first spray device 20 is positioned above the belt 16 and in alignment with the spray coating station 14, the arrangement being such that when the belt 16 stops the cylindrical shell 11 is coaxially positioned beneath the spray device 20.

At this point, it is merely necessary to cause relative axial movement'between the shell 11 and the spray device 20 so that the spray head 22 axially traverses the shell. In order to facilitate an understanding of the present 1nvention, in the present form hereinbelow described the spray device 20 is stationary and is mounted on a fixed structural member (not shown), while the cylindr1cal shell 11 is moved vertically upward about the spray head 22.

In order to permit relative axial movement between the cylindrical shell 11 and the spray head 22, the illustrative spray coating station 14 is provided with a pair of oppositely facing C-shaped brackets 60 (best illustrated in FIG. 2) which are respectively disposed on e1ther side of the conveyor belt 16. Each of the C-shaped brackets 60 includes a pair of upright posts 62 having annular flanges 63 formed adjacent the upper ends thereof, such flanges normally being disposed at the level of or slightly below the level of the upper surface of the belt 16. The arrangement is such that when the belt 16 is stopped with a cylindrical shell accurately positioned in the spray coating station 14, the lower peripheral edge 61 of the shell is disposed immediately above the two pairs of flanges 63. As 'best shown in FIG. l, the brackets 60 are coupled to the actuating plunger 65 of a suitable fluidactuated piston and cylinder arrangement, here fragmentarily shown at 66. It will, of course, 'be understood by those skilled in the art that any suitable control means can be provided for actuating the piston and cylinder assembly 66 in timed relation to starting and stopping of the conveyor belt 16, and, consequently, it should not be necessary to describe herein the details of such well known and conventional control systems. Rather, it should sufce to point out that when the piston and cylinder arrangement 66 is energized to project the plunger 65 vertically upward, the C-shaped brackets 6l) are raised, thereby firmly seating the cylindrical shell 11 on the flanges 63 and raising the shell 11 olf of the conveyor belt 16. As the shell 11 approaches the spray head 22, the latter is turned on so as to initiate a centrifugal spray coating operation with the spray head rotation for example, being as shown. Continued vertical upward movement of the shell 11 causes the spray head 22 to relatively traverse the axial length of the shell, thereby applying a uniform coating to the internal surface of the latter. When the shell 11 has completely traversed the spray head 22, the latter is deactivated and the lluid connections to the piston and cylinder arrangement 66 are reversed, thereby returning the plunger 65, brackets 60, and shell 11 towards their lowermost position as shovm in FIG. 1. If desired, a second coating can be applied to the inner surface of the shell during downward vertical movement of the latter.

In keeping with the invention a second spray device 20' including a rotatable spray head, generally indicated at 22', is positioned above the belt 16 and in alignment with the spray coating station 15. The arrangement being, as in the rst station, such that when the belt stops the cylindrical shell 12 is coaxially positioned beneath the spray device 20'. The second spray coating station is also provided with a pair of oppositely facing C-shaped brackets 60 having a pair of upright posts 62 with annular flanges 63 formed adjacent the upper ends thereof. When the belt is stopped with a cylindrical shell positioned in the spray coating station 15, the lower peripheral edge 61 of shell is disposed immediately above the two pairs of flanges 63. A control system similar to the one described in connection with the first spray coating station 14 is utilized with the second station 15; however, in this instance, the spray head 22' rotation is in a direction opposite to that of spray head '22 (i.e., spray head 22 rotates counterclockwise and spray head 22 rotates clockwise as viewed in FIG. l).

In accordance with one of the important aspects of the present invention, provision is made for utilizing the same basic spray head and associated equipment for each of the oppositely rotating spray devices, yet wherein only the single expedient of simply having the distributor dimensioned to uniformly distribute spray material to its associated discs in accordance with the direction of rotation of the distributor is required. In order to achieve this result, as best shown by reference to FIGS. 4, 5, 6 and 7 conjointly, the distributor teeth 41 are angled slightly, opposite to the direction in which rotation of the distributor occurs, Thus, the distributor 38 shown in FIG. 4 or 5 is intended for rotation in a counterclockwise direction as illustrated FIG. 8. The distributor 37' illustrated in FIGS. 6 and 7, however, is intended to rotate in the opposite or clockwise direction. In either instance, the distributor rotating in its respective direction will continuously apply a uniform coating of spray material to its adjacent discs as hereinbefore described.

In order to more fully understand the mode of operation of the exemplary centrifugal spray system, reference is now made to FIG. l wherein the apparatus is shown with shell 11 positioned along belt 16 beneath the spray device 20. Shell 12 is also shown positioned along belt 16 beneath spray device 20 but it may be considered to have already been coated in spray station 14 and awaits a subsequent coating application in spray Station 15. At the start of the cycle, shell 11 is raised oft" the conveyor belt and spray head 22 relatively traverses the axial length of the shell applying a uniform coating to the internal surface of the latter with the spray head rotating, for example, in the direction shown. After the shell has completely traversed the spray head 22, it is returned to position along the conveyor as shown in FIG. 1 and the conveyor advances the shell to spray station 15 and stops. The shell 11 is now raised upwardly to traverse spray head 22', which is rotated in a direction opposite to that of spray head 22. When the shell has completely traversed the spray head 22 the latter is deactivated and the shell is returned to the conveyor belt. This cycle repeats itself for each shell positioned along the conveyor belt.

It will be appreciated by those skilled in the art that under normal operating procedures it is desirable to permit flow of the spray material through the nozzles 45 only during those periods when the spray head 22 are positioned within the shells 11, 12 thereby preventing loss of spray material and undesirable application of the material to the outer surface of the shell and other objects in the immediate vicinity of the spray station 14. Unfortunately, however, each time that the ow of spray material is stopped, the material accumulated on the distributor 38 (FIG. 3) and the spray discs Dl-DS is expelled from the spray device 2i). Therefore, each time that a spray coating operation is initiated, a definite delay is encountered during which the distributor and spray discs are again charged to their full capacity. During the charging period, the density of the spray emanating from the spray head is gradually built up to a maximum level. As a consequence of the foregoing, the coating applied tothe inner surfaces of the cylindrical shells 11, 12 during the initial charging period is less dense than that applied once the spray head 22 is charged to full capacity. In the past it had been either necessary to accept such deviations in coating uniformity, or alternatively, it had been necessary to charge the spray head prior to the time that the latter enters the shell thereby resulting in a loss of spray material and possible undesirable coating of environmental objects.

In order to eliminate the delay time that had previously been encountered in charging centrifugal spray heads to full capacity, thereby permitting application of a uniform coating to the entire inner surface of the cylindrical shell rapidly and without loss of spray material at either end of the shell, provision is made in the exemplary centrifugal spray device for initially injecting -a substantial overcharge of spray material into the cavity (FIG. 3) so that the distributor and disc surfaces are substantially in- I stantaneously charged to full capacity. To this end, and as best illustrated in FIG. 1, the illustrative spray system includes a second pump 44 for supplying spray material under pressure from the source 42 to a second nozzle 45' which is also adapted to inject such spray material into the distributor cavity 40.

Thus, it will be appreciated that when a spray coating operation is initiated, it is merely necessary to inject spray material into the spray head through both nozzles 45, 45' simultaneously, thereby charging the spray heads to full simultaneously, thereby charging the spray heads to full capacity substantially instantaneously. Having fully charged ow of spray material to the spray heads to a level sufficient to thereafter maintain the spray heads charged at full capacity during continued operation thereof. This can, of course, be accomplished simply by shutting off the flow to one of the nozzles 45, 45" as, for example, by turning off or deactivating the pump 44. Alternatively, this same result could be achieved by reducing the flow of spray material through both nozzles until the desired level is reached, and this could be accomplished by utilizing one or more pumps 44 having a conventional accelerator control, the details of which are well known to those skilled in the art and need not be further described in the present application. It will, of course, be understood that the length of time required to charge the spray head to full capacity will depend upon various considerations such as the size of the spray head, the nature of the spray material, and the capacity of the pump or pumps employed. However, once the foregoing variables are selected, the length of time required to charge the spray head to full capacity can be readily determined, and the pump or pumps can thereafter be either manually or automatically controlled by any suitable conventional means so as to insure that each time a spray operation is initiated, a sufficient overcharge of spray material is initially provided for the purpose of charging the spray heads to full capacity as rapidly as possible.

Turning now to FIG. 9 there is shown a slightly modified centrifugual spray system which is quite similar in construction and operation to that shown in FIG. l, and also embodies certain of the features of the apparatus shown in FIG. 1. However, in the exemplary apparatus shown in FIG. 9 a uniform coating of spray material is applied to the interior surfaces of cylindrical shells with spray particles applied at a first direction and subsequently applying spray particles from a direction opposite to the first direction without the necessity of shifting the container to a second spray station.

In carrying out this form of the invention, a first centrifugal spray device a is positioned in alinement with and above the spray coating station 14a in the same manner as hereinbefore described. A second centrifugal spray device 2017 is positioned in alinement with and below the spray coating station 14a. The spray heads 22a, 22b of spray devices 20a, 20]; respectively are substantially identical, however, spray head 22b is inverted and rotates in a direction opposite to the direction of rotation of spray head 22a.

In the present instance, in order to apply a uniform coating of spray material with the sprays projected at opposite directions to avoid gaps about surface irregularities and the like, the shell 11a is positioned coaxially between the spray heads 22a, 22b. At this point, it is merely necessary to cause relative axial movement between the shell 11a and each of the oppositely rotated spray heads 22a, 22b. It should be understood that the shell could be held stationary While the spray heads successively are passed axially therethrough. Moreover, it should be understood that the order in which relative axial Amovement between each of the spray heads and the shell is not critical to the present invention and may be varied without deviating therefrom.

It will be apparent from the foregoing that there has herein been disclosed a novel centrifugal spray coating 12 system employing apparatus and methods which, although characterized by their simplicity and reliability, serve .to insure uniformity of the coating applied to a workpiece. Not only does the unique arrangement of distributor and spray disc contribute to such coating uniformity, but, moreover, there has herein been disclosed improved methods for applying spray particles to the workpiece at generally opposite directions whereby the coating applied is uniform throughout the entire area of coverage, yet wherein the applied coating is free from gaps, voids or thinned areas in regions of surface irregularities, contours or openings and the like.

I claim as my invention:

1. The method of internally coating a cylindrical surface comprising the steps of positioning a first centrifugal spray head adjacent one end of the surface and coaxial therewith, rotationally driving the spray head in a first direction centrifugally projecting spray material from the periphery of said spray head along lines in a direction opposite to the direction of rotation of said first head, translating the spray head axially relative to surface, charging the spray head with a constant flow of spray material during relative translation of the head through said surface, positioning a second centrifugal spray head adjacent one end of the surface and coaxial therewith, rotationally driving the second spray head in a second direction opposite to said first spray head rotational direction centrifugally projecting spray material from the periphery of said second spray head along lines in a direction opposite to the direction of rotation of said second head, and translating the second spray head axially relative to the surface while charging the second spray head with a constant flow of spraying material thereby applying a coating of substantially uniform thickness from opposite directions throughout the entire faxial length of the cylindrical surface.

2. A centrifugal spray coating system for applying a uniform coating to a cylindrical surface throughout substantially the entire axial length of the surface, said system comprising, in combination, first and second spray heads, ra source of spray material, means for effecting relative coaxial translation of each of said spray head successively through the cylindrical surface to be coated, means for rotationally driving said first spray head in a first direction centrifugally projecting spray material from the periphery of said spray head along lines in a direction opposite to the directions of rotation of said first spray head, means for driving said second spray head in a second direction opposite to said first spray head rotational direction centrifugally projecting spray material from the periphery of said spray head along lines in a direction opposite to the direction of rotation of said second spray head, and means for charging the spray head with a constant flow of spray material drawn from said source, thereby applying a coating of substantially uniform thickness applied from opposite directions throughout the entire length of the surface.

3. A centrifugal spray coating system for applying a uniform coating to the internal surface of a cylindrical shell throughout substantially the entire axial length of the latter, said system comprising, in combination, first and second spaced apart centrifugal spray heads, a source of spraying material for each of said heads, means for rotationally driving said first spray head in a first direction centrifugally projecting spray material from the periphery of said spray head along lines in a direction opposite to the direction of rotation of said first spray head, means for rotationally driving said second spray head in a direction opposite to said first spray head direction centrifugally projecting spraying material from the periphery of said second spray head along lines in a direction opposite to the direction of rotation of said second spray head, means for charging the spray heads With -a constant flow of spray material drawn from respective sources, means for advancing said shell to said first spray head adjacent one end of said shell and coaxial therewith, means for effecting relative coaxial translation of said rst spray head through the cylindrical surface to be coated, said advancing means positioning said second spray head adjacent one end of said shell and coaxial therewith, means for effecting relative coaxial translation of said second spray head through the cylindrical surface to be coated thereby applying a coating of substantially uniform thickness at oppositely sprayed directions throughout the entire length of the surface.

4. A centrifugal spray coating system as claimed in claim 3 wherein said spray heads are positioned above the shells to be coated and said means for advancing the shells shifts the shell from a position beneath that rst spray head to a position beneath that second spray head.

S. A centrifugal spray coating system as claimed in 14 claim 3 wherein said first spray head is positioned above said shell and said second spray head is positioned below said shell.

References Cited UNITED STATES PATENTS 2,103,270 12/1937 Murch 118-314 3,011,472 12/1961 Kent et al 117-9342 X 3,017,116 l/1962 Norris 239-224 X ALFRED L. LEAVI'IT, Primary Examiner CHARLES R. WILSON, Assistant Examiner U.S. Cl. X.R. 

